The present invention relates to a magnetic bubble memory module, and in particular, to such a module suitable for minimizing the module thickness and the power loss.
A magnetic bubble is a small cylindrical magnetic domain which appears in a crystal film in which the direction of magnetization in the crystal film is perpendicular to the film surface because of the strong magnetic anisotropy of the cryatal film made of a rare-earth orthoferrite or a magnetic garnet. Since the magnetic bubble can be controlled with an external magnetic field or electric current to be moved freely along the inner surface of the crystal film, functions such as a compact memory and a logic will be developed by using the magnetic bubble phenomenon.
A magnetic bubble memory was reported from the Bell Telephone Laboratories in 1967. The bubble memories have advantages that since no mechanical movable components are involved, high-speed operation and high reliability are attained as compared with magnetic tapes or disks and that since it is nonvolatile, a high-density memory can be manufactured through a rather simpler process as compared with IC memories. Therefore, the bubble memory has been used as an auxiliary storage of an electronic switching system as well as a memory for terminal equipments or microcomputers.
FIG. 1 depicts a partially cutaway view in perspective of a conventional bubble memory module, and FIG. 2 illustrates a cross section taken along line II--II of FIG. 1. Referring to these figures, a wiring board 2 is provided with a magnetic bubble memory chip 1 thereon and has external terminals 3 at an end portion thereof. On the board 2 is mounted an annular rectangular parallelepiped core 5 of soft magnetic material which is provided with a winging 4 on each of four sides thereof. The chip 1 is placed in a space defined by the annular rectangular parallelepiped core 5. A shielding conductor case 6 as disclosed in U.S. Pat. No. 4,165,535 is disposed to cover as a whole the chip 1, the windings 4 and the core 5 excepting the external terminals 3. A set of a magnet plate 7 and a magnetic shunt plate 8 is provided on each of top and bottom surfaces of the case 6. Numerals 10 represent spacers. A tubular magnetic shielding case 9 is disposed to cover the whole assembly.
As is apparent from FIG. 2, the height H.sub.1 of the thus constructed magnetic bubble module is determined by the respective thicknesses of the magnetic shielding case 9, the magnet plate 7, the magnetic shunt plate 8, the shielding conductor case 6, the board 2 with the chip 1 mounted thereon, and the core 5 having the windings 4 disposed thereon.
Since magnetic bubble modules have been widely adapted in various devices or systems, it becomes indispensable to minimize the module size especially for small-sized equipment, and the reduction of the module thickness as well as a decrease of the loss have been highly desired.
When minimizing the module thickness and the loss in the case of the module structure shown in FIGS. 1 and 2, if the thickness t of the winding 4 is increased in order to reduce the loss P, the module height H.sub.1 increases. On the other hand if the thickness t of the winding 4 is decreased in order to minimize the module height H.sub.1, the loss P increases. Thus, the simultaneous attainment of the minimization of the module thickness and the minimization of the loss is impossible in this module structure. In FIG. 7, a curve 16 represents a relationship between the module height H and the loss P for the module structure shown in FIGS. 1 and 2. A point 19 on the curve 16 shows that the loss P is equal to P.sub.1 when the module height H is H.sub.1. The module height H is limited to H.sub.1 in this structure.